The present invention relates generally to seals, such as seals for rotary machines, and more particularly to method for making a brush-tooth seal.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor shaft, or the rotor blade (i.e., bucket) tips, of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor shaft, or the rotor bucket (i.e., blade) tips, of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Tooth seals are known, such as labyrinth and vernier seals, which have any number of longitudinally spaced-apart and inward-pointing seal teeth. Brush-tooth seals, in the form of brush-labyrinth seals, are known wherein a longitudinally-middle, labyrinthseal tooth is replaced with a brush seal. Steam and gas turbines have positioned a labyrinth seal between the rotating rotor shaft, or the rotating bucket or blade tips, and the circumferentially surrounding stator casing to minimize fluid-path leakage. Steam and gas turbines also have positioned brush seal bristles between the rotating shaft and the circumferentially surrounding stator casing to minimize fluid-path leakage. It has been proposed, in steam and gas turbines, to use a brush-tooth seal positioned between the rotating rotor shaft and the circumferentially surrounding stator casing. In a brush-tooth seal, the brush seal is considered the primary seal because of its better sealing capabilities, and the tooth seal is considered the secondary (or backup) seal.
The conventional method for making a brush-tooth seal for a rotary machine begins with obtaining a seal carrier having a shape of generally a first annular circumferential arc, having a longitudinal axis, having a circumferentially extending and radially-inward-opening groove, and having longitudinally spaced-apart, circumferentially extending, and radially-inward-protruding seal teeth. A brush seal is then obtained having a shape of generally a second annular circumferential arc engageable with the groove. The brush seal is then moved in a circumferential direction about the longitudinal axis during which time an EDM wire, moving in a longitudinal direction, cuts the tips of the bristles at a generally identical predetermined distance from the longitudinal axis. The brush seal, with the cut bristle tips, is then engaged in the groove and attached to the seal carrier. One or more of the finished seal carriers then would be installed in a turbine stator to form a circular brush-tooth ring seal. A typical turbine could have seven or eight ring seal locations.
Applicants found that when approximately seven circular brush-tooth ring seals were installed in a particular turbine, that turbine experienced excessive rotor vibrations and was automatically shut down within approximately fifteen minutes of startup by the vibration trips located on the turbine bearings. When all such seals were removed, Applicants found the turbine would start. What is needed is to solve the problem of being able to use a brush-tooth seal in a rotary machine.